1. Field of the Invention
The invention relates to an inductor for the simultaneous inductive heating of two tracks or ways which are arranged next to one another at a distance and which are formed on a metallic workpiece, the inductor having a first segment which is associated with the first track or way and a second segment which is associated with the second track or way, and having two supply arms via which the segments of the inductor can together be connected to a power supply.
As well as this, the invention also relates to a particularly advantageous use of such inductors.
2. Description of the Related Art
Inductors of the kind being considered here are used in machines for hardening portions of metallic workpieces, by a hardening operation which may if required be carried out in rotation, to bring that portion of the workpiece which is to be hardened at the time to the hardening temperature. A cooling fluid is then applied to the portion which has been heated at the time and this cooling fluid cools the portion concerned so quickly that a hardened microstructure forms therein.
Inductors of the kind specified in the opening paragraph, which are also known as “double inductors” in the specialist vocabulary, are used in practice to enable inductive heating which is time-saving and energy-efficient to be carried out with only simple equipment in the case of workpieces on which tracks or ways extending in parallel are to be hardened. The inductors which are used for this purpose have two segments which are connected in series and of which one is associated with one of the tracks or ways to be heated and the other is associated with the other track or way. The supply of power takes place in this case via a connection which is provided at the side of the double inductor.
Large double-row ball bearings have grooves which serve as tracks for the particular rolling elements and these grooves can be heated to whatever hardening temperature is required in the given case in a particularly efficient way with inductors of this kind. The tracks of rolling bearings of this kind need to be sufficiently hard to be able to withstand in the long term the high and locally closely confined compressive loads which occur in operation. The ridge which is present between the tracks and which guides the rolling elements needs, on the other hand, to be sufficiently tough to be able to safely absorb the transverse forces which occur in operation without the risk of its fracturing.
To harden the tracks of such large double-row ball bearings, the two tracks are heated simultaneously with a double inductor. In contrast to hardening of the two tracks in succession, this gives increased throughput despite the fact that only one power source is used. Also, tempering effects in both directions, which may occur as a result of heat conduction when hardening takes place in succession, are avoided.
However, there is a disadvantage to the simultaneous inductive heating of tracks or ways extending in parallel with one another which are separated by a material portion which is generally of a strip-like or ridge-like form, namely that the material portion situated between the tracks or ways is also covered by the electromagnetic field induced by the inductor. The resultant heating may be sufficiently extensive for a hardened microstructure to form across the entire width of the material portion situated between the tracks or ways which are to be hardened.
This effect is found to be particularly critical when what are being hardened are the tracks of double-row rolling bearings in which the distance between the tracks is small, or in other words the ridge left between them is comparatively thin. If the ridge is hardened throughout, it loses the toughness it needs and there may be a fracture of the material as a result of the loads occurring in operation.